Add new date_bin_wallclock SQL functions

[sanderson]

Related to https://github.com/influxdata/influxdb_iox/issues/12681

Adds the following SQL functions to the Serverless, Dedicated, and Clustered docs:

• date_bin_wallclock
• date_bin_wallclock_gapfill

---

• Rebased/mergeable

[jstirnaman]

Missing URL

[mhilton]

"Daylight Saving Time" and "British Summer Time" aren't equivalents. DST refers to the general concept of adjusting the local time to make the most of the daylight hours. BST is a time zone offset identifier. I think this should be reworded a little to express that.

[sanderson]

@mhilton Thanks. Is there a generalized term you use in the UK to represent the 1 hour seasonal offset? Is it just Daylight Savings Time? In the US, we have the general "DST," but we also have timezone-specific offset identifiers (Pacific Standard Time (PST) vs Pacific Daylight Time (PDT)).

[mhilton]

Yes it's very similar, but in the UK we only have to worry about one time-zone so they can be used haphazardly. The concept is known as "Daylight Saving Time" which changes the timezone from "GMT" to "BST".

[appletreeisyellow]

Suggested change

	date_bin_wallclock(interval, expression[, origin])
	date_bin_wallclock(interval, expression[, origin_timestamp])

The arguments defined below uses origin_timestamp. To keep wording consistent, maybe changing the word to origin_timestamp here, or changing the word to origin below?

[appletreeisyellow]

It would be good to highlight a caveat:

Using an origin and interval such that there are bins within a discontinuity, but which do not align with the point at which the discontinuity occurs, can produce unexpected results. For example, considering the following query:

SELECT date_bin_wallclock(INTERVAL '1 hour', tz('2020-10-25T02:29:00+01:00', 'Europe/Paris'), '1970-01-01T00:30:00') AT TIME ZONE 'UTC';

The result is:

2020-10-24T23:30:00Z

However, the result of a nearly identical query:

SELECT date_bin_wallclock(INTERVAL '1 hour', tz('2020-10-25T02:30:00+01:00', 'Europe/Paris'), '1970-01-01T00:30:00') AT TIME ZONE 'UTC';

is:

2020-10-25T01:30:00Z

That is, timestamps only one minute apart are placed into bins that are two hours apart, despite the expected interval being one hour. Care should be taken to avoid such scenarios.

[mhilton]

In general advice to try and stay away from the discontinuities is probably sensible.

[jstirnaman]

👍 , pending other reviewer suggestions.